Hydraulic feedback system



March 18, 1969 P. F. HAYNER ET AL 3,433,126

HYDRAULIC FEEDBACK SYSTEM Filed on. 19. 1966 v Sheet 1 of 4 IERT 3Z9 1 2MANUAL lNPUT A ,ns 1

"\s w l FEEDBACK MECHANICAL JI B L i U@ 1 ACTUATOR LINKAGE SUPPLY RETURNl a 4 1| 22 r I L r 7 l 2' m I g g I s R INPUT L A 2? a A' RETURN aNEUTRAL I |9 I V VALVE l PosmoN L FEEDBACK VALVE J r PRESSURE 1- 2o W1CYLINDER 1 I4 I l OUTPUT I HYDRAULIC NEUTRAL l3" LOAD POWER POSITIONACTUATOR A vs J 23 V L 24 V////// /i Fl (5. l.

mvsmons PAUL F. HAYNER LAWRENCE W. SHARPE A T'TORNEY March 18, 1969 P.F. HAYNER ETAL 3,433,126

HYDRAULIC FEEDBACK SYSTEM Filed Oct. 19, 1966 Sheet 3 of 4 21 O I IMANUAL I I INPUT l 1 2 30 I I 9 V HYoRAuuc FLUID I I MECHANICAL I iL'NKAGE SUPPLY RETURN I I Q --I ---f 36 [I 92 :5 H49 37 m 3% L 1 Q r 21x3 %32d 1 'o non/Q32: FEEDBACK l ZL C 4 Q PRESSURE 1- 5 36 l 57 49 20 56CYLINDER 0+ l I 4 l I HYDRAULIC l OUTPUT NEUTRAL #5 POWER PosmoNACTUATOR ,ll

VALVE I 24 I 23 LL a INVENTORS PAUL F. HAYNER LAWRENCE W. SHARPE ATTORIJE'Y March 18, 1969 P. F. HAYNER ET AL 3,433,126

HYDRAULI C FEEDBACK SYSTEM Filed Oct. 19, 1966 Sheet 3 of 4 INVENTORSPAUL F. HAYN ER LAWRENCE W. S RPE :5; f

ATYORNEY United States Patent Oflice 3,433,126 Patented Mar. 18, 19693,433,126 HYDRAULIC FEEDBACK SYSTEM Paul F. Hayner, Lexington, Mass.,and Lawrence W. Sharp, Glencliif, N.H., assignors to Sanders Associates,Inc., Nashua, N.H., a corporation of Delaware Filed Oct. 19, 1966, Ser.No. 661,151 US. Cl. 91-367 17 Claims Int. Cl. FlSb 13/16, 9/10 ABSTRACTOF THE DISCLOSURE A hydraulically operated mechanism for positioning aremote load in accordance with the position of a local input member.Movement of the input member operates a control valve which transmitsfluid pressure to an actuator which displaces the load and also actuatesa mechanism which transmits feedback fluid pressure which repositionsthe control valve. Errors which accumulate due to leakage, fluidexpansion due to temperature, etc. are corrected each time the systembecomes static with both the input member and the load in their centralor zero displacement positions.

This invention relates to hydraulic feedback systems and, moreparticularly, to hydraulic position feedback systems including means foreliminating and correcting position drift in the system.

Hydraulic position feedback systems generally include a mechanicallyactuated control valve by which hydraulic fluid is delivered from asupply source to an output actuator and through which return fluid fromthe actuator is delivered to the source. Such systems include positionfeedback means which also controls the valve but in an opposite sense tothe manual control. Thus, the feedback is negative feedback. As oftenoccurs in such systems, changes in the load, hydraulic leakage orchanges in the volume of the hydraulic feedback system due to changes intemperature, result in an error in the position feedback.

It is one object of the present invention to provide a hydraulicposition feedback system in which said errors are eliminated and/orcorrected.

It is another object of the present invention to provide a hydraulicposition feedback system including means whereby changes in therelationship between input control position and load position areeliminated and/or corrected.

It is another object of the present invention to provide an improvedhydraulic position control system.

In van application of the present invention, a hydraulic feedback systemis provided for administering a control action to the main hydrauliccontrol valve which controls the flow of hydraulic fluid to and from anoutput actuator in such a manner that the actuator positions a load topositions corresponding to the position of the main valve controlmechanism. The sense of the feedback control applied to the valve issuch that the valve feeds hydraulic fluid to the actuator whichpositions the load until the load reaches a'position corresponding tothe position of the control mechanism. As this corresponding position isreached, the feedback system administers a control action to the valvewhich cuts off the flow of the hydraulic fluid through the valve to theactuator.In the present invention, means are provided to eliminate thefeedback action each time the valve control mechanism is positioned atthe neutral or zero position. In applications where the feedback is ahydraulic pressure, feedback is eliminated at the zero position byconnecting the feedback pressure to a reference pressure source selectedto represent zero feedback. This is accomplished employing one or moreneutral position valves in series which connect the feedback pressure tothe reference pressure and is operated by the output actuator.

For example, if the requirement for system gain is sufiiciently low, asingle neutral position valve operated by the output actuator may beemployed to open the feedback pressure line to the reference pressureeach time the actuator is positioned at neutral. On the other hand, ifthe system gain requirement is relatively high, the phase lag betweeninput and output at increasing response rates may best be solved by twoneutral position valves in series. In this case, the first neutralposition valve is operated by the main valve control mechanism and openswhen the mechanism is positioned at the neutral position, and the secondneutral position valve is actuated by the output actuator and opens whenthe load is positioned at the neutral position. These two valves areconnected in series and open the hydraulic feedback line to thereference pressure so that the feedback system is neutralized andprovides neither positive nor negative feedback to the main controlvalve.

In the various embodiments of the invention described herein, thefeedback system includes a spring loaded piston. Hydraulic fluid atconstant pressure (reference pressure) is provided to one side of thepiston and hydraulic fluid at variable pressure is provided to the otherside of the piston. The variable pressure fluid is obtained from afeedback pressure piston which is mechanically actuated by the outputactuator so as to provide greater and greater hydraulic fluid pressureto the second side of the feedback system as the output actuator movesin the given direction. The unbalanced pressure across the feedbackpiston causes the piston to move until the unbal anced pressure isopposed and balanced by the spring forces, and this movement is appliedto the main control valve as the feedback thereto. In the presentinvention, when the input control mechanism and the load are positionedat their neutral positions, equal pressures are applied to both sides ofthe feedback piston and so the feedback piston provides no feedback tothe main control valve.

Hydraulic position control systems, such as described above, in normaluse are operated through the neutral position many times during eachhour of operation. Employing the present invention, each time the systemis operated through the neutral position, feedback errors which arisefor reasons already stated are eliminated. For example, the steering anddiving controls on a submarine will go through the neutral position onthe average about once a minute, and since the temperature change of thehydraulic fluid in one minute is comparatively small and leakage is alsosmall, the one minute interval between corrections is adequate.

Other objects and features of the present invention will be apparentfrom the following specific description taken in conjunction with thefigures in which:

FIG. 1 is a block diagram of a hydraulic position control systemincorporating features of the present invention;

FIG. 2 is a block diagram of a hydraulic position control systemincorporating features of the present invention and includes a sectionalview of one form of the main control valve;

FIG. 3 is a sectional view of one arrangement of parts of the hydraulicsystem illustrated in FIG. 1 and illustrates a main control valve andfeedback system slightly different from that illustrated in FIG. 2;

FIG. 4 is an enlarged sectional view of a portion of FIG. 3; and

FIG. 5 is a sectional view of a control system similar to thatillustrated in FIG. 2.

Turning first to FIG. 1 there is shown a block diagram which illustratesa typical hydraulic control system which is manually controlled andwhich positions a load. This system is equipped with position feedbackand includes means for eliminating the position feedback when in theneutral position. The input mechanism 1 of the system is controlled bymanipulation of the manual input 2 which actuates a mechanical linkage3. Mechanical linkage 3 simultaneously actuates the supply valve 4, areturn valve 5 and the input neutral position valve 6. These valves 4, 5and 6 are effectively ganged and operated together by, for example, asingle actuating mechanism 7 from the mechanical linkage 3. The gangedvalves are referred to by the reference number 8.

The ganged valves 8 are controlled by the mechanism 7 so that a manualcontrol in the positive direction 9 of the manual input 2 causes thesupply valve 4 to feed hydraulic fluid from the supply portion of thehydraulic fluid source 10 from port S to port A of the supply valve 4.At the same time, the return valve 5 is actuated to feed returnhydraulic fluid from port A to port R which returns the fluid to thereturn portion of the source 10.

Port A of the supply valve 4 feeds hydraulic fluid to one side of thehydraulic power actuator 11 which includes a ram piston connected by themechanism 12 to load 13 causing the load to move in the positivedirection denoted by arrow 14.

On the other hand when the manual input 2 is moved in the negativedirection indicated by arrow 15, the mechanism 7 causes the supply valve4, ports S and B to connect and causes the return valve 5, ports R and Bto connect. Thus, hydraulic fluid from the supply is delivered to theopposite side of the hydraulic powered actuator ram causing the load 13to move in the negative direction indicated by the arrow 16.

Position feedback in the system described so far can i be accomplishedin a variety of ways. One way of accomplishing position feedback isillustrated in the figure. For example, a feedback actuator 17 which ismechanically part of the input mechanism 1 can be employed. The actuator17 is hydraulically powered and applies a mechanical action 18 whichcombines with the output from the manual input 2 to control themechanical linkage 3. The feedback actuator 17 responds to movement ofthe load in such a manner that a movement of the load in the positivedirection in response to a manual input in the positive direction causesthe feedback actuator 17 to provide a mechanical input to the mechanicallinkage which tends to oppose the manual input to the mechanicallinkage, or tends to reduce the effect of the mechanical input from themanual input 2 to the mechanical linkage 3. Thus, the feedback isnegative. The feedback effectively turns off the supply and returnvalves 4 and 5 so that there is no flow of hydraulic fluid between theactuator 11 and the source 10 even through the manual input remainsstationary at a positive position or a negative position.

For the purpose of controlling the feedback actuator 17, a feedbackpressure cylinder 19 is provided. The piston in the pressure cylinder 19is mechanically connected by mechanism 20 to the ram in the actuator 11so that motion of the ram, in for example, the positive direction,causes the piston in the cylinder 19 to increase the pressure in thehydraulic feedback line 21 connected to the feedback actuator 17.

The hydraulic feedback pressure in line 21 opposes the supply(reference) pressure fed to feedback actuator 17 via line 22 and,depending upon which pressure is greater, causes the feedback actuatorto move one way or another against a spring load. This movementcontinues until the spring load counter balances the unbalancedpressure. The action of the feedback cylinder is response to movement ofthe output ram, the design of the feedback actuator and its springloading, the design of the supply and return valves and the mechanicallinkage thereto are all such that the position of the load in the plusdirection and minus direction on each side of the zero positioncorresponds to the position of the manual input in the plus and minusdirections on each side of its zero position. The feedback is such thatonce the load is positioned to a position which corresponds with themanual input position, all flow of hydraulic fluid betwen the actuator11 and the source 10 stops, effectively locking the actuator 11 inposition.

As can be seen, from the above description of the system, changes in themagnitude of the load 13, changes in the relative temperature betweenthe fluid in lines 21, 22 and 25 and internal or external leakage offluid from lines 21, 22 and 25 will all introduce an error in the systemso that the magnitude of feedback Will drift. In accordance with thepresent invention, this situation is remedied by valving means whichconnect the line 25 to the supply. This effectively neutralizes thefeedback actuator each time the system is positioned at the neutral orzero position. For this purpose, there is provided the input neutralposition valve 6 controlled by the mechanism 7 and the output neutralposition valve 23 which is controlled by mechanical connection 24 to theram in the power actuator 11. Thus, valve 6 is controlled by the inputto the system and valve 23 is controlled by the output from the system.The feedback line 21 is opened to the supply portion of the source 10(reference pressure) via valve 6, line 25 and valve 23 each time themanual input 2 and the load 13 simultaneously move through their zero orneutral positions, thereby correcting the feedback errors introduced tothe system for reasons already stated. For convenience, the actuator 11,load 13, feedback cylinder 19 and output neutral position valve 23 arepreferably at the same location and constitute the output mechanism 26.

' The system described above includes two neutral position valves 6 and23 and is preferred when the requirements for system gain is relativelyhigh. If system gain is relatively low, the input neutral position valvemay be eliminated (bypassed) so that only a single valve, 23, connectsthe feedback line 21 with the supply of source 10. The inherentlygreater stability of the low gain system permits use of the singleneutral position valve controlled by the output actuator 11 to open eachtime the actuator is positioned at neutral.

FIG. 2 illustrates a similar embodiment of the invention in which thesupply valve, the return valve and the input neutral position valve areformed in an integral unit shown in cross section and referred to hereinas the main control valve. As shown in FIG. 2, the output mechanism 26at one location is the same as in FIG. 1. This includes the hydraulicpower actuator 11 driving the load 13 and the feedback pressure cylinder19 and output neutral position valve 23 which are operated by mechanicalconnection to the ram of the actuator 11 just as already described withreference to FIG. 1. The input mechanism 27 including the manual input28, mechanical linkage 29 and hydraulic fluid source 30 may also besimilar to correspondingly named parts in FIG. 1.

In operation, the manual input 28 is positioned to, for example, a plusposition by movement in the direction of arrow 31 and this movement istransmitted via the mechanical linkage 29 to the main spool 32. inthevalve 33. A positive motion of the manual input in the direction ofarrow 31 causes the main spool 32 to move in a positive directionindicated by arrow 34. The spool 32 moves within a cylindrical sleeve 35which is slideably mounted within the valve block 36. The sleeve ispositioned within the valve block by springs 37 and 38 at each end ofthe sleeve which bear against both the sleeve and the valve block. Thesprings 37 and 38 are enclosed Within cavities 39 and 40, respectively,to which hydraulic fluid is fed which also tends to position the sleevewithin the block, the final position of the sleeve within the blockbeing determined by the spring tensions and the magnitude of the fluidpressures in the cavities 39 and 40.

Hydraulic fluid ports 41 to 49 are provided in the block. Port 41 feedshydraulic fluid (reference pressure) from the supply of the source 30 tothe cavity 39 and port 49 feeds fluid from feedback line 21, which ispressurized by the feedback pressure piston 19, to the cavity 40. Thus,the differential pressure acting upon the sleeve within the valve blockis a function of the displacement of the load from the zero or neutralposition. This function may be a linear function such that thedifferential is zero when the load is at the zero position and increaseslinearly as the load is displaced in the positive direction indicated byarrow 14. Correspondingly, as the load is displaced in the negativedirection indicated by arrow 16, the direction of the differential isreversed and also changes proportional to the magnitude of thedisplacement from the zero position. Thus, negative position feedback isprovided.

The ports 42 to 48 are at least in partial registry at all times withthe ports 51 to 57, respectively, in the sleeve 35. Ports 42 and 44connect to the return of the hydraulic fluid source 30 and ports 41, 43and 45 connect to the supply of the hydraulic fluid source. The purposeof the sections 32a to 320? of the spool 32 sliding within the sleeve 35is to gate the flow of hydraulic fluid between the source 30 and theactuator 11 and between the source and feedback line 21 via the outputneutral position valve 23. Thus, the functions of supply valve 4, returnvalve 5 and input neutral position valve 6 in FIG. 1 are all performedby the main control valve 33 and position feedback is applied to thisvalve via line 21 as a hydraulic fluid pressure rather than a mechanicalactuation as in FIG. 1.

If system gain is sufficiently low, or the system is inherentlyexceedingly stable, the input neutral position valve may be eliminatedand so valve 23 may be connected directly to the supply of the source 30(reference pressure). Thus, in such a low gain system, the valve 33 maybe substantially simplified and the feedback system requires only onehydraulic line between the output mechanism 26 and the valve 33.

In operation, when the spool 32 is moved in the positive directiondenoted by arrow 34, port 51 is blocked, port 52 is opened feedingsupply fluid through port 55 to the actuator 11, and port 53 is openedfeeding hydraulic fluid from the actuator 11 through ports 56 and 53 tothe return of the source 30. This causes the ram of the actuator 11 tomove and displace the load 13 in the positive direction denoted by arrow14. At the same time, the ram moves the piston in the feedback cylinder19 decreasing the pressure of fluid in line 21 which changes theunbalance of pressure on the sleeve within the block causing the sleeveto move relative to the block in the direction of arrow 34. Thus, themotion of the spool to uncover ports and permit hydraulic fluid to flowto the actuator causing the actuator to move is compensated for as thefeedback causes the sleeve to move in the same direction as the spool.When the actuator 11 is at a position corresponding to the concurrentposition of the manual input 28, the compensation is complete and thesupply and return of the source 30 are block from the actuator 11.

The ports 54 and 57 in thesleeve 35 are positioned so that when there isno unbalanced hydraulic pressure on the sleeve within the block 36 andwhen the spool 32 is at the zero or neutral position of the manualinput, these ports align with the narrow annular groove 58 between thespool sections 320 and 32d so that supply fluid pressure is applied tothe output neutral position valve 23. The groove 58 and ports 54 and 57combine to define the input neutral position valve which performs thesame function as valve 6 in FIG. 1.

Valve 23 opens when the load is at the zero or neutral position andcauses hydraulic fluid supply pressure to be applied to line 21. Thiseffectively connects the cavities 39 and 40 which drive the sleeve inthe block to the same supply pressure and so the sleeve is positionedonly by the springs 37 and 38. Thus, it is seen that each time thesystem moves through the zero or neutral position the effect of feedbackis made zero thereby eliminating the feedback egrlors due to thepreviously mentioned time changing varia es.

FIGS. 3 and 4 illustrate still another embodiment of the inventionincluding parts which correspond substantially to the various parts inthe block diagram of FIG. 1. In this embodiment, the feedback is bothhydraulic and mechanical, just as in FIG. 1, and is applied from thefeedback actuator 61 to the main control valve '62 by moving thefloating fulcrum 63 of the mechanical linkage 64 which connects themanual input 65 to the valve. The main control valve 62 provides thefunctions of the supply valve 4, return valve 5 and the input neutralposition valve 6 of FIG. 1. Also, the feedback pressure actuator 66performs the functions of the feedback pressure cylinder 19 and outputneutral position valve 23 in FIG. 1.

In operation, the manual input 65 is operated by rotating the handle 67which translates a nut 68- along a screw 69 and the screw moves a lever70 about the input fulcrum 71. This in turn moves the main valve lever73 about the floating fulcrum 63 and positions the spool 74 within thevalve housing 75. The spool 74 includes four sections 74a and 74d.Section 7411 meters hydraulic fluid from the supply cavity 76 to one orthe other of ports 77 or 78 which connect with the lines 79 feeding theload actuator 82. The spool sections 74a and 740 meter flow between theports 77 and 78 and the return cavities 80 and 81.

The actuator 82 includes a cylinder 83 and ram or piston 84 which drivesthe lever 85 about the output fulcrum 86 so as to position the positiveacting piston 87 and neutral position valve 88 in the position actuator66. The piston 87 pressurizes hydraulic fluid in the cavity 87a whichconnects to one side 89 of the feedback piston 90 in the feedbackactuator 61 via feedback line 91. The other side 92 of the feedbackpiston is fed directly from the hydraulic fluid supply.

In operation, when the manual input 65 is operated so that the nut 68travels along the input scale 93 in the positive direction or to apositive position, lever 73 is moved so that the main spool piston 74];opens port 77 to fluid supply pressure. At the same time, piston 74copens port 78 to the return 81. This causes the output ram to move inthe positive direction as indicated on the output scale 94 and move thepiston 87 so as to decrease the pressure on side 89 of the feedbackpiston 90 which moves in the negative direction indicated by arrow 95and displaces the floating fulcrum 63 in the negative direction. Thisshift of the fulcrum 63 in the negative direction, indicated by arrow95, effectively cancels the manual control action on the spool 74 sothat the flow of hydraulic fluid between the output actuator 82 and thesupply and return cavities of valve 62 is stopped. This locks the outputram in position. Thus, it is seen, the hydromechanical position feedbackis negative feedback and causes the output scale reading to follow theinput scale reading.

The neutral or zero position correction to the feedback system isaccomplished by connecting the cavity 87a (which controls the positionof t e feedback piston) to the supply or reference pressure. The cavity87a is connected to supply pressure when the neutral position valve 88opens. This valve opens when the annular groove 96 in the feedbackpressure piston 87 is in registry with the ports 97 and 98 which connectthe cavity 87a to supply a pressure via the input neutral position valve99, shown enlarged in FIG. 4. The input neutral po-s'tion valve 99 isformed between spool sections 740 and 74d or by an opening 100 betweenthese sections which provides passage between the underlapped pistonports 101 and 102. Thus, whenever the output ram 84 moves through theneutral or zero position as indicated on the output scale 94, and at thesame time the main spool of valve 62 is manually positioned at or verynear the input neutral position as indicated on scale 93, the left side89 of the piston 90 is connected to supply pressure thereby reducing thepressure differential across the feedback piston 90 to zero so that thefeedback piston is positioned by the springs 103 and 104 loaded therein.This places the fulcrum 63 at the zero or neutral position. By placingthe fulcrum at the zero position each time the system goes throughneutral, the drift in the feedback caused, for example, by changes inthe load driven by the actuator 82 or leakage of fluid from the pressureactuator 66 or the feedback actuator 61 is eliminated.

If the requirement for system gain is sufliciently low or the system isinherently very stable, the function of the input neutral position valve99 may be eliminated. In this case, port 98 of the position actuator 66would connect directly to supply pressure so that valve 99 is bypassed.This would reduce the total number of hydraulic lines running betweenthe actuators 82 and 66 and the main control valve 62 to a minimum ofthree The underlapped piston ports 101 and 102 of the input neutralposition valve 99 and the annular opening 160 between the pistonsections 740 and 74d of the main spool are dimensioned to provide a zeroposition deadband region of this valve equal to the deadband region ofthe valve 88 formed in the feedback pressure actuator 66. A reasonablerequirement for this deadband region is 0.5% of the overall positioningrange. This is a reasonable requirement, for example, for the hydraulicsteering and diving control of a submarine. The dwell time of such ahydraulic positioning system at any particular position is at least 0.1second. Accordingly, in the submarine steering and diving controlsystems, the dimensions of the input neutral position valve 99 and theoutput neutral position valve 88 as well as the fluid lines betweenthese valves and the feedback actuator 61 are suflicient so that thecorrection to the floating ground position may be accomplished withinthe 0.1 second dwell time.

FIG. illustrates in sectional view an embodiment incorporatingstructural features shown in FIGS. 2 and 3. In this embodiment, the maincontrol valve 110 is substantially identical to valve 33 and theposition feedback to this valve is all hydraulic just as in FIG. 2.Feedback pressure is applied to the cavity 112 at one end of sleeve 113mounted slide'ably within the valve block 114. The feedback fluid inline 115 is pressurized by the feedback piston 116 driven within thefeedback piston cylinder 117 by a mechanical coupling 118 which connectsthe piston to the output ram 119 of the output actuator 120. Thus, themovement of the piston 116 is proportional to the movement of the load121 by the output ram 119 and is in such a direction as to providenegative feedback.

The valve 110 is operated manually by positioning the lever 122 about aspring centered fulcrum 123 so that an arm 124 connecting the lever tothe valve spool 125 positions the spool within the sleeve 113. Thefulcrum 123 is centered by the spring operated actuator 126 which may becontrolled by a mechanism 127 for imposing a bias on the system. Themechanism 127 may be electrically, mechanically, hydraulically, orpneumatically operated and preferably imposes a predetermined scheduleof operation on the system which may vbe overridden at any time byoperation of the manual input lever 122. For example, if the system isused to control the diving or steering control surfaces of a submarine,the mechanism may be automatically controlled in response to submarinedepth or heading as detected by appropriate transducers. Thus, in thismanner, the system would operate as an automatic pilot subject at anytime to being overridden by the human operator.

A bias mechanism such as 127 may also be employed in the system shown inFIG. 3 to add a third control action to the mechanical linkage 64 whichpositions the spool 74 to control the hydraulic flow to and from theload actuator 82. In this case, the mechanical linkage is not a simplelever as shown, but preferably takes the form of the so called tripodinput lever described in copending application entitled, Multi-Arm LeverMechanism, by Paul F. Hayner and Lawrence W. Sharpe, Ser. No. 587,893,filed on even date herewith and assigned to the same assignee as is theinstant application.

The tripod input lever feeds three mechanical actuations to the spool ofthe main control valve; these are the manual input from a device such as65, a feedback actuation from a feedback actuator such as 61 and a biasactuation from a bias actuator such as 126 which is controlled by a biasmechanism such as 127. All three actuations are instrumental, via thetripod input lever, to position the spool in the main control valve.

The tripod input lever is so constructed that the manual input canoverride both the feedback and the bias. Since the bias can represent apredetermined schedule of operation, the system can operate as anautomatic pilot subject to being overridden by the human operator.

Referring again to FIG 5, the spool section 125b meters supply fluidfrom the supply cavity 128, which connects the hydraulic fluid source,to the ports 129 and 130, which connect to one side or the other of theoutput actuator 129. At the same time, one of the return fluid cavities131 or 132 is blocked and so fluid is returned from the other side ofthe actuator to the source. This causes the ram 119 to move the load 121and to actuate the mechanical coupling 118 which in turn moves thefeedback piston 116 in such a direction as to change the pressure inline 115 and cavity 112 in such a sense that the sleeve 113 moves in thesame direction that the spool has just moved which in sequence blocksthe supply cavity 128 and return cavities 131 and 132 within the mainvalve block.

An annular groove 133 in the feedback piston 116 combines with ports 134and 135 in the cylinder 117 to define the output neutral position valve136 and the groove 137 between spool pistons 1250 and d combines withports 138 and 139 in the sleeve to define the input neutral positionvalve 140. Port 138 connects to the supply cavity 128 and port 139connects to the output neutral position valve 136.

In operation, when both the input, 140, and output, 136, neutralposition valves are open, cavity 112 is connected to the supply orreference pressure just as the cavity 141 and so the sleeve is returnedto the neutral position by the centering springs 142 and 143. Thisoperation is the same as in valve 38 in FIG. 2. The dimensions of thegroove on the main spool piston sections 1250 and 125d and the ports 138and 139 and the dimensions of the output neutral position valve 136 aresuch that a significant calibration correction is made each time thesystem is at or near the neutral position. If, for example, the deadbandportion is l /2% of maximum stroke and the output ram feedback has aboutsix percent position error, the system must course through the zero orneutral position four times to make a complete calibration correction ofthe neutral position.

This completes descriptions of a number of embodiments of the presentinvention of a hydraulic position system including position feedbackwhich may be administered to the input of the system hydro-mechanicallyor all hydraulically and in which means are provided for effectivelycancelling the feedback so that the feedback is zero each time thesystem is positioned at a neutral position, thereby correcting feedbackerrors introduced by changes in the trapped hydraulic volume due toexternal or internal leakage across the system seals, changes in volumedue to changes in the system load, or changes in the trapped volume dueto rapid changes in temperature of the hydraulic fluid.

What is claimed is:

1. A hydraulically operated positioning system comprising:

(A) a source of pressurized hydraulic fluid,

(B) means for driving a load,

(C) means for controlling the flow of said hydraulic fluid to saiddriving means,

(D) feedback means coupling said driving means to said control means,

(E) whereby said driving means and said control means function insynchronism moving together to related positions, and

(F) means for inactivating said feedback means when said driving meansis at a predetermined position.

2. A hydraulically operated positioning system comprising:

(A) A source of pressurized hydraulic fluid,

(B) means for driving a load,

(C) means for controlling the flow of said hydraulic fluid to saiddriving means,

(D) feedback means coupling said driving means to said control means,

(E) whereby said driving means and said control means function insynchronism moving together to related positions, and

(F) means for inactivating said feedback means when said driving meansand said control means are each in a predetermined position.

3. A system as in claim 2 in which:

(A) said predetermined positions of said driving means and said controlmeans are their respective neutral positions.

4. A system as in claim 3 and in which:

(A) said control means comprises mechanically controlled valve having amechanical input thereto, and

(B) said feedback means mechanically connects to said mechanical input.

5. A system as in claim 3 and in which:

(A) said control means includes a hydraulically driven valve, and

(B) said feedback means connects hydraulically to said valve.

6. A system as in claim 3 and in which:

(A) said feedback means includes means for producing a feedback fluidpressure representative of the position of said driving means,

(B) feedback actuator means responsive to said feedback pressure, and

(C) means coupling said feedback actuator means to said control means.

7. A system as in claim 6 and in which:

(A) said means for inactivating said feedback means includes means forsubstantially nullifying the effect of said feedback pressure on saidfeedback actuating means.

8. A system as in claim 7 and in which:

(A) said means for nullifying includes a valve which connects saidfeedback pressure to a reference pressure to cause said nullification.

9. A system as in claim 7 and in which:

(A) said means for nullifying includes two valves in series whichconnect said feedback pressure to a reference pressure to cause saidnullification.

10. A system as in claim 8 and in which:

(A) said means for nullifying includes at least two valves in serieswhich open said feedback pressure to said source pressure to cause saidnullification.

11. A system as in claim 7 and in which:

(A) said feedback actuator means includes a spring centered feedbackpiston which mechanically connects to said control means, and

(B) said feedback piston is driven against said springs by the hydraulicpressure differential between said feedback pressure and said sourcepressure.

12. A system as in claim 10 and in which:

(A) the first of said two valves in series is controlled by said controlmeans, and

(B) the second is controlled by said driving means.

13. A system as in claim 10 and in which:

(A) said driving means, said means for producing said feedback pressureand said second valve are formed in an integral unit.

14. A system as in claim 10 and in which:

(A) said control means, said feedback actuator means and said firstvalve are formed in an integral unit and said driving means, said meansfor producing said feedback pressure and said second valve are formed inanother integral unit.

15. A system as in claim 2 and further including:

(A) manually operated means connected to said controlling means, and

(B) biasing means connected to said controlling means and responsive toa preselected parameter,

(C) whereby said manually operated means can be actuated by an operatorto override said biasing means in the operation of said system.

16. A system as in claim 15 and in which:

(A) said biasing means comprises a hydraulic bias signal, a hydraulicbias actuator responsive thereto and means connecting said bias actuatorto said controlling means.

17. A system as in claim 15 and in which:

(A) said biasing means comprises an electrical bias signal, a biasactuator responsive to said bias signal and means connecting said biasactuator to said controlling means.

References Cited UNITED STATES PATENTS 2,320,508 6/1943 Burns et a1.91-388 3,171,330 3/1965 McCornbs 91-338 3,283,669 11/1966 Lissau 91388FOREIGN PATENTS 42,494 5/ 1933 France.

PAUL E. MASLOUSKY, Primary Examiner.

US. Cl. X.R.

